TWI431833B - Electric energy storage device - Google Patents

Description

Power storage device

The present invention relates to a power storage device having a large capacitance.

A power storage device having a positive electrode, a negative electrode, and a non-aqueous electrolyte as a main component has been proposed, and has been put into practical use in power storage and power storage systems for mobile devices, and standby power supplies for personal computers. Among them, a storage device using an electric double layer using graphite as a positive electrode material and a carbonaceous material as a negative electrode material is superior in electric capacity and withstand voltage as compared with a conventional electric storage device using activated carbon as an electrode (refer to Patent Document 1) ).

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-294780

The electric double layer power storage device described in Patent Document 1 is excellent in electric capacity and voltage resistance as described above, but a power storage device having a larger capacitance is still expected.

As a result of deliberate research to solve the above problems, the present inventors have found that a power storage device including a cathode material containing graphite, a negative electrode material containing a specific metal oxide, and an electrolytic solution has a large capacity and safety. The invention is excellent in qualitative and safety, and the present invention can be completed.

That is, the present invention is a cathode material containing graphite containing at least one selected from the group consisting of Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sb, Bi, W, and Ta. A negative electrode material of an oxide of a metal element and a power storage device for an electrolytic solution.

Since the electricity storage device of the present invention uses a negative electrode material containing a specific metal oxide, the electric capacity is increased. The cathode material containing graphite can be charged and discharged at a high voltage to achieve high energy density. In particular, in the present invention, high output is achieved by using graphite as a positive electrode and a specific metal oxide as a negative electrode.

The power storage device of the present invention is characterized by comprising: a cathode material containing graphite, containing a material selected from the group consisting of Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sb, Bi, W, and Ta a negative electrode material of an oxide of at least one metal element, and an electrolyte.

In the present invention, as the negative electrode material, an oxide of at least one metal element selected from the group consisting of Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sb, Bi, W, and Ta is used. . When the metal oxide of at least titanium is used as the oxide of the metal element, the capacitance can be increased, which is preferable. Further, in the case of using an electrolyte containing a lithium salt, if the oxidation-reduction potential of lithium is 0 V, the oxidation-reduction potential of the metal oxide containing titanium is about 1 to 2 V, which is so high for lithium. The precipitation of metallic lithium to the negative electrode can be suppressed, so that safety is also high, and more preferably titanium oxide and a composite oxide of titanium and an alkali metal or alkaline earth metal element. The composite oxide may, for example, be lithium titanate/calcium titanate, barium titanate or strontium carbonate, or a layered alkali metal titanate represented by M ₂ Ti ₃ O ₇ (M represents an alkali metal). The shape of the particles may be any of an isotropic shape such as a spherical shape or a polyhedral shape, an anisotropic shape such as a rod shape, a fiber shape, or a sheet shape, and is not particularly limited. Further, insofar as the effect of the present invention is not impaired, the surface of the oxide of the undoped other impurity metal or the surface of the oxide may be an inorganic substance such as cerium oxide or aluminum oxide, a surfactant, and a coupling agent. The organic matter is subjected to surface treatment.

Among the above metal oxides, titanium oxide is particularly preferred because of its crystal lattice stability. Further, the titanium oxide in the present invention contains a compound of titanium and oxygen, a hydrogen-containing compound, an aqueous compound, or a hydrate, and examples thereof include titanium oxide (titanium dioxide, titanium oxynitride, titanium oxide, etc.), and titanium. Acid compound (dihydrogenitride (metadanic acid), tetrahydrogenitride (orthotitanic acid), H ₂ Ti ₃ O ₇ with H _4x/3 Ti _(2-x)/3 O ₄ (x= a layered titanate compound represented by 0.50 to 1.0) or the like, titanium hydroxide (such as titanium tetrahydrogen oxide), or the like. The particle diameter of the titanium oxide is not particularly limited, and a high output input consideration is required. Preferably, the specific surface area is in the range of 0.1 to 500 m ² /g.

In the present invention, as the titanium oxide, a crystallized or amorphous type such as a rutile type, a brookite type, an anatase type, a bronze type, or a ramsdellite type may be used. Alternatively, anatase type and/or rutile type titanium oxide is preferred because it has a higher capacitance than other titanium oxides. Particularly preferably, the anatase type has a specific surface area of 5 to 500 m ² /g, and particularly preferably in the range of 5 to 350 m ² /g. Further, it is more preferable that the rutile type has a specific surface area of 50 to 500 m ² /g, and particularly preferably in the range of 50 to 350 m ² /g.

Alternatively, a titanium oxide obtained by heating a layered titanate compound may be used. Specifically, the titanium oxide described in the specification of Japanese Patent Application No. 2007-221311 and Japanese Patent Application No. 2007-223722 can be cited. In other words, the titanium oxide described in Japanese Patent Application No. 2007-221311 is a layered titanic acid compound represented by H ₂ Ti ₃ O ₇ in a temperature range of 200 to 350 ° C (at a temperature higher than 260 ° C, The titanium oxide is described in the specification of 2007-223722 as the pair of H _4x/3 Ti _(2-x)/3 O ₄ (x). The layered titanic acid compound represented by =0.50 to 1.0) is heated and fired in a temperature range of 250 to 450 ° C.

Titanium oxide can be used by assembling primary particles into secondary particles. The secondary particles in the present invention are in a state in which the primary particles are strongly bonded to each other, and are not aggregated or mechanically compacted by intergranular phase interaction such as van der Waals force, and are usually mixed, disintegrated, and filtered. Industrial washing under water washing, transportation, weighing, bagging, stacking, etc. does not easily disintegrate, and almost all exist in the state of secondary particles. The amount of voids of the secondary particles is preferably in the range of 0.005 to 1.0 cm ³ /g in the battery characteristics, and more preferably in the range of 0.05 to 1.0 cm ³ /g. The average particle diameter of the secondary particles (the 50% median diameter obtained by the laser scattering method) is preferably in the range of 0.5 to 100 μm in terms of electrode production.

Further, when the average particle diameter of the primary particles (the 50% median diameter obtained by electron microscopy) is in the range of 1 to 500 nm, the desired amount of voids is easily obtained, and it is more preferably in the range of 1 to 100 nm. The specific surface area is not particularly limited, and is preferably in the range of 0.1 to 200 m ² /g, and particularly preferably in the range of 3 to 200 m ² /g. Further, the shape of the particles is not limited, and various shapes such as an isotropic shape and an anisotropic shape may be used.

Further, in the present invention, a titanium oxide having a particle shape of a sheet may be used, and the flaky particles usually include a plate, a sheet, or a flake. The size of the flaky particles is preferably in the range of 1 to 100 nm in thickness and 0.1 to 500 μm in width and length. Alternatively, fine flaky particles called nanosheets may be used, and the thickness is in the range of 0.5 to 100 nm, and the width and length are preferably in the range of 0.1 to 30 μm, respectively, in the range of 0.5 to 10 nm in thickness, and width. A range of 1 to 10 μm in length is more preferable.

Next, the graphite used for the positive electrode material in the present invention is not particularly limited. In the present invention, "graphite" means a range in which d ₍₀₀₂₎ obtained by the peak position of the X-ray diffraction 002 plane is 0.335 to 0.344 nm. Among them, graphite having a specific surface area of 0.5 to 300 m ² /g is preferred, and a range of 5 to 100 m ² /g is more preferable.

As the electrolytic solution for immersing the above positive electrode and negative electrode, for example, a solute may be dissolved in a nonaqueous solvent. The anion acting as an electrolyte may be selected from the group consisting of 4 fluorinated boronic acid ions (BF ₄ ^- ), 6 fluorinated phosphate ions (PF ₆ ^- ), perchloric acid ions (ClO ₄ ^- ), and 6 arsenic fluoride ( AsF ₆ ^-), ₆ antimony fluoride (SbF ₆ ^-), perfluoro acyl methanesulfonamide (CF ₃ SO ₂ ^-), mesylate perfluorinated group (CF ₃ SO ₃ ^- group of) consisting of at least One.

Further, as the cation, a group consisting of a symmetrical four-stage ammonium ion, an ethylmethylimidazolium salt, a spiro-(1,1') bispyridinium salt, or the like, and a lithium ion may be selected. in. Among them, those containing lithium ions are preferred.

Further, as the nonaqueous solvent, it may be derived from tetrahydrofuran (THF), methyltetrahydrofuran (MeTHF), formaldehyde, ethyl acetate, diethyl carbonate, dimethyl ether (DME), propylene carbonate (PC), γ-butyl Carbene such as lactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), acetonitrile (AN), ring At least one selected from the group consisting of butyl sulfonium (SL) or a non-aqueous solvent containing fluorine as one of the molecules.

The power storage device of the present invention includes the positive electrode, the negative electrode, the electrolytic solution, and a separator, and specific examples thereof include an electrochemical capacitor, a hybrid capacitor, a redox capacitor, an electric double layer capacitor, and a lithium battery. In the positive electrode and the negative electrode, a conductive material such as carbon black, acetylene black or ketjen black, and a binder such as a fluororesin or a water-soluble rubber resin may be added to the positive electrode material and the negative electrode material, and appropriately obtained by molding or coating. The separator may be a porous polyethylene film polypropylene film or the like.

[Examples]

The embodiments of the present invention are disclosed below, but the present invention is not limited thereto.

(Example 1) (Manufacture of positive electrode)

A graphite (1) having d ₍₀₀₂₎ of 0.3371 nm and a powder obtained by mixing with acetylene black and a polytetrafluoroethylene resin obtained by X-ray diffraction (trade name: TAB, manufactured by The Bulgarian Central Laboratory of Electrochemical Power Source Co., Ltd.) The mixture was mixed at a weight ratio of 3:1, kneaded by an agate mortar, and formed into a circular shape having a diameter of 10 mm to obtain a pellet. The weight of the particulate matter was 10 mg. The pellet was superposed on a screen made of aluminum as a current collector cut into a diameter of 10 mm, and pressed at 9 MPa to obtain a positive electrode (1).

(Manufacture of negative electrode)

Anatase type titanium dioxide, acetylene black, and tetrafluoroethylene resin having a specific surface area of 314 m ² /g were mixed at a weight ratio of 5:4:1, kneaded by an agate mortar, and formed into a circular shape having a diameter of 10 mm to obtain a pellet. The weight of the granules was 15 mg. The pellets were laminated with a copper foil having a diameter of 10 mm as a current collector to obtain a negative electrode (1).

(Manufacture of power storage device)

The positive electrode (1) and the negative electrode (1) were vacuum dried at 200 ° C for 4 hours, and then assembled into a sealable coin type test cell in a globe box having a dew point of -70 ° C or lower. The test unit was made of stainless steel (SUS316) having an outer diameter of 20 mm and a height of 3.2 mm. The positive electrode (1) is placed in a lower tank of the evaluation unit under the current collector, and a polypropylene film as a separator is placed thereon, and 1 mol is dropped as a non-aqueous electrolyte from above. The /L concentration dissolves a mixed solution of ethylene carbonate and ethyl methyl carbonate of LiPF ₆ (mixed in a volume ratio of 3:7). The current collector is placed on the upper negative electrode (1) and a spacer of 0.5 mm thick for thickness adjustment and a spring (all manufactured by SUS316), and the upper can with the acryl gasket is stacked thereon. The edge portion was tightly sealed to obtain the electricity storage device (sample A) of the present invention.

(Examples 2 to 6)

A power storage device of the present invention was obtained in the same manner as in Example 1 except that the anatase type titanium oxide having a specific surface area of 314 m ² /g in Example 1 was changed to various titanium oxides shown in Table 1. Sample B~F).

(Example 7)

20.0 g of commercially available rutile-type high-purity titanium dioxide (PT-301: manufactured by Ishihara Sangyo Co., Ltd.) and 8.85 g of sodium carbonate were mixed, and then fired in an electric furnace at 800 ° C for 20 hours in the air, and then again. The mixture was heated and fired under the conditions to obtain a layered sodium titanate having a composition of Na ₂ Ti ₃ O ₇ . To the obtained layered sodium titanate, a 1 mol aqueous hydrochloric acid solution was added to a concentration of 10 g/L to carry out a reaction for 4 days. As a result of analyzing the reaction product, almost no sodium was contained, so that sodium was almost completely substituted by hydrogen, and it was confirmed that a layered titanic acid compound having a composition of H ₂ Ti ₃ O ₇ was obtained. Further, in the reaction, the aqueous hydrochloric acid solution was changed every other day. The obtained layered titanic acid compound was filtered, washed, and solid-liquid separated, and dried in air at 60 ° C for 12 hours, and then heated in an air at 280 ° C for 20 hours in the air to obtain titanium oxide. Sample g). Further, the sample g was measured in a temperature range of 300 to 600 ° C by a differential thermal balance to obtain a heating loss of 1.0% by weight. When the amount of heat loss is estimated to be from the crystal water contained in the titanium oxide, it is considered to be a titanic acid compound having a composition of H ₂ Ti ₂₂ O ₄₅ . Further, as a result of measuring the X-ray diffraction pattern of the sample g by the Cu-Kα line as a radiation source, a pattern similar to the bronze type titanium dioxide shown by JCPDS card 35-088 or the like was exhibited. However, in the bronze type, two peaks of the (001) plane and the (200) plane are observed around the diffraction angle (2θ) of 15°, and in the sample h, the interval between the two peaks is 0 or very close. The X-ray diffraction pattern of the sample g is shown in Fig. 1. The electricity storage device (sample G) of the present invention was obtained in the same manner as in Example 1 except that the titanium oxide was changed to the sample g in the first embodiment.

(Example 8)

The ratio of K/Li/Ti molar ratio to 3/1/6.5 is determined by using potassium carbonate, lithium carbonate, and rutile-type titanium dioxide obtained by neutralizing and hydrolyzing titanium tetrachloride as a titanium oxide. Mix and grind thoroughly. The ground material was transferred to a white gold crucible, and fired in an electric furnace at 800 ° C for 5 hours in the air to obtain a layered lithium potassium titanate having a composition of K _0.8 Li _0.27 Ti _1.73 O ₄ . To the obtained layered lithium potassium titanate 1 g, 100 cm ³ of hydrochloric acid having a concentration of 1 equivalent was allowed to react at room temperature for 1 day while stirring. As a result of analyzing the reaction product, almost no lithium or potassium was contained, and lithium and potassium were almost replaced by hydrogen, and it was confirmed that the composition was a layered titanic acid compound having a composition of H _1.07 Ti _1.73 O ₄ . Then, it was filtered, washed with water, and dried, and then heated at 400 ° C for 20 hours in the air to obtain titanium oxide (sample h). The measurement of the heating loss of 300 to 600 ° C of the sample h was 0.12% by weight. It is estimated that the sample is a composition of H ₂ Ti ₁₈₉ O ₃₇₉ as in the case of Example 8, and it is considered to be almost titanium dioxide (TiO ₂ ). Further, as a result of measuring the X-ray diffraction pattern of the sample h by the Cu-Kα line as a radiation source, a pattern similar to the bronze type titanium dioxide shown by JCPDS card 35-088 or the like was exhibited. However, in the bronze type, two peaks of the (003) plane and the (-601) plane can be observed around the diffraction angle (2θ) of 44°, and in the sample h, the interval between the two peaks is 0 or very close. . The X-ray diffraction pattern of sample h is shown in Fig. 2. The electricity storage device (sample H) of the present invention was obtained in the same manner as in Example 1 except that the titanium oxide was used as the titanium oxide in the first embodiment.

(Example 9)

The layered titanic acid compound having a composition of H _1.07 Ti _1.73 O ₄ obtained in Example 8 in an amount equivalent to 0.4 g of TiO _{2 was} added and dissolved in an amount of H ⁺ relative to the layered titanic acid compound. In an amount of 100 cm ³ of an aqueous solution of tetrabutylammonium hydroxide in an amount of 100 rpm, the vibrator was shaken to the extent of 150 reciprocations/min for 10 days, thereby peeling off the layered titanic acid to obtain anatase-type flaky titanium oxide. As a result of measurement by a scanning probe microscope, the width and length were about 0.2 to 1.0 μm, and the maximum thickness was about 1.5 nm. The electricity storage device (Sample I) of the present invention was obtained in the same manner as in Example 1 except that the flaky titanium oxide was used as the titanium oxide.

(Embodiment 10)

Anatase-type titanium dioxide having a specific surface area of 314 m ² /g obtained in Example 1 was dispersed in pure water by a juicer to be liquefied, and 5% by weight of TiO ₂ equivalent to the aqueous titanium hydroxide was added. After the polyvinyl alcohol (Houpar PVA-204C: manufactured by Kuraray) aqueous solution, pure water was further added and adjusted to a concentration of 10% by weight in terms of TiO ₂ . This slurry was spray-dried by a four-fluid nozzle type spray dryer (MDL-050B type: Fujisawa Electric Mechanism) at an inlet temperature of 200 ° C, an outlet temperature of 80 ° C, and an air discharge amount of 80 L/min. particle. The obtained secondary particles are heated and calcined in air at a temperature of 500 ° C for 3 hours, and then the heated calcined product is repulped with pure water, filtered, washed, solid-liquid separated, classified, and dried to obtain a sharp Secondary particles of titanium oxide type titanium dioxide. The average primary particle diameter (50% diameter of the volume basis obtained by electron microscopy) was 7 nm, and the average secondary particle diameter (50% diameter of the volume basis obtained by the laser scattering method) had an average secondary particle diameter of 9.2. Nm, the amount of voids is 0.552 cm ³ /g. A power storage device (sample J) of the present invention was obtained in the same manner as in Example 1 except that the secondary particles were used as the titanium oxide.

(Example 11)

Except for the anatase type titanium dioxide having a specific surface area of 314 m ² /g instead of the layered titanic acid compound having the composition of H ₂ Ti ₃ O ₇ obtained in Example 7, as the negative electrode active material, In the same manner, the electricity storage device (sample K) of the present invention was obtained.

(Embodiment 12)

The layered sodium titanate having the composition of Na ₂ Ti ₃ O ₇ obtained in Example 7 was used as a composite oxide containing titanium and an alkali metal in place of anatase type titanium dioxide having a specific surface area of 314 m ² /g, and the particulate matter was A power storage device (sample L) of the present invention was obtained in the same manner as in Example 1 except that the weight was 60 mg.

(Examples 13 to 20)

In place of graphite (3) having a d ₍₀₀₂₎ of 0.3368 or a graphite (3) having a d ₍₀₀₂₎ of 0.3363 obtained by X-ray diffraction instead of the graphite (1) used in Examples 1 to 3, The electricity storage device (samples M to T) of the present invention was obtained in the same manner as in the first embodiment.

(Comparative Example 1)

A power storage device (sample U) to be compared was obtained in the same manner as in Example 1 except that commercially available activated carbon was used instead of titanium dioxide as the negative electrode material in Example 1.

(Comparative Example 2)

A power storage device (sample V) to be compared was obtained in the same manner as in Example 1 except that the commercially available activated carbon used in Comparative Example 1 was used instead of graphite (1) as the positive electrode material.

Evaluation 1: Determination of specific surface area

The specific surface areas of the positive electrode material and the negative electrode material used in Examples 1 to 20 and Comparative Examples 1 and 2 were measured by a BET method using a specific surface area measuring apparatus (Monosorb: manufactured by Yuasa-Ionics). The results are shown in Table 1.

Evaluation 2: Evaluation of capacitance

The electric capacities of the electricity storage devices (samples A to V) obtained in Examples 1 to 20 and Comparative Examples 1 and 2 were evaluated. For each sample, the charger was set to a constant current of 0.3 mA, and after charging for 2 hours up to 3.5 V as the charging voltage, the discharge capacity at the time of discharge to 0.3 mA and 1 V was used as the sample. The capacity (mAh/g (positive active material)) is shown in Table 2. Further, the discharge curves of the samples A to L, N, and R are shown in Figs. The discharge curve, the voltage axis slice, the capacitance slice and the area enclosed by the origin are equivalent to the energy of the power storage device, and the larger the area, the greater the energy.

Evaluation 3: Cycle characteristics

The power storage devices (samples A to L) obtained in Examples 1 to 12 were subjected to cycle characteristic evaluation. For each sample, the charge/discharge current was set to 0.3 mA, and after charging at a constant current of 3.3 V, the discharge was performed to 1.0 V in the same manner, and the charge and discharge cycle of 30 cycles was repeated. The charge and discharge capacities of the second cycle and the 30th cycle were measured, and as the respective capacities, (the capacity of the 30th cycle / the capacity of the second cycle) x100 was used as the reusability. The results are shown in Table 3. Further, the change in the capacity retention rate of Example 1 is shown in Fig. 19.

Evaluation 4: Evaluation of power characteristics

The power storage devices (samples A, B, D, G, I, and J) obtained in Examples 1, 2, 4, 7, 9, and 10 were evaluated for power characteristics. Each sample was charged and discharged in a range of a voltage range of 1.0 to 3.3 V, a charging current of 40 mA/g, and a discharge current of 40 to 1600 mA/g, and each of the discharge capacities was measured. The capacity retention rate is calculated by measuring the discharge capacity of 40 mA/g as X ₁ and measuring the value of X _n in the range of 80 to 1600 mA/g by (X _n /X ₁ )x100. Calculate the formula. The results are shown in Table 4. It can be determined that even if the amount of current is increased, excellent power characteristics can be obtained as long as the capacity retention rate is high.

(Example 21) Manufacture of the positive electrode

3 g of graphite (1) used in Example 1, 1 g of acetylene black and tetrafluoroethylene mixed powder (TAB), kneaded in an agate mortar, pressed on an aluminum substrate, and punched into a circle having a diameter of 12 mm. A positive electrode (2) having a mass of 10 mg and a thickness of about 0.1 mm was obtained.

Manufacture of negative electrode

³ g of anatase titanium dioxide having a specific surface area of 314 m ² /g and TAB1g used in the examples were kneaded by an agate mortar, pressed on an aluminum substrate, and punched into a circle having a diameter of 12 mm to obtain a living matter quality. 10 mg of a negative electrode (2) having a thickness of about 0.1 mm.

Manufacture of power storage devices

The electricity storage device of the present invention (sample A) was obtained in the same manner as in Example 1 except that the positive electrode (1) and the negative electrode (1) in Example 1 were changed to the positive electrode (2) and the negative electrode (2), respectively. ').

(Examples 22 to 29)

A power storage device of the present invention was obtained in the same manner as in Example 21, except that various titanium oxides shown in Table 5 were used instead of the anatase type titanium oxide having a specific surface area of 314 m ² /g in Example 21. B'~I').

Evaluation 5: Determination of specific surface area

The specific surface area of the titanium oxide used in Examples 21 to 29 was measured in the same manner as in Evaluation 1. The results are shown in Table 5.

Evaluation 6: Evaluation of capacitance

The electric capacities of the electricity storage devices (samples A' to I') obtained in Examples 21 to 29 were evaluated. After the charging current is applied to the power storage device of the sample A' to I' at a constant current of 1 mA, the voltage is switched to a constant voltage at a point of 3.5 V for a total of 2 hours of charging, and then discharged to lmA and 0 V to discharge the discharge capacity. The capacitance (mAh/g (positive electrode active material)) as a sample is shown in Table 6.

The power storage device of the present invention has a large capacity. Further, as seen in the comparison of Examples 4, 5, and 12 and Comparative Example 1, in the present invention, even if the capacitance is not too large, since the discharge voltage is high, the energy is large. Therefore, it can be seen that high energy density can be achieved. Moreover, the reusability characteristics and power characteristics are also excellent.

(industrial availability)

The power storage device of the invention is useful for a power source for a mobile body such as an electric vehicle or a power storage system for an electric power business.

1 is an X-ray diffraction pattern of a titanium oxide (sample g) obtained in Example 7.

2 is an X-ray diffraction pattern of titanium oxide (sample h) obtained in Example 8.

Fig. 3 is a graph showing the discharge of the electricity storage device (Sample A) obtained in Example 1.

4 is a discharge graph of the electricity storage device (sample B) obtained in Example 2.

Fig. 5 is a graph showing the discharge of the electricity storage device (sample C) obtained in the third embodiment.

Fig. 6 is a graph showing the discharge of the electricity storage device (sample D) obtained in the fourth embodiment.

Fig. 7 is a graph showing the discharge of the electricity storage device (sample E) obtained in Example 5.

Fig. 8 is a graph showing the discharge of the electricity storage device (sample F) obtained in Example 6.

Fig. 9 is a graph showing the discharge of the electricity storage device (sample G) obtained in the seventh embodiment.

Fig. 10 is a graph showing the discharge of the electricity storage device (sample H) obtained in Example 8.

Fig. 11 is a graph showing the discharge of the electricity storage device (Sample I) obtained in Example 9.

Fig. 12 is a graph showing the discharge of the electricity storage device (sample J) obtained in Example 10.

Fig. 13 is a graph showing the discharge of a power storage device (sample K) obtained in Example 11.

Fig. 14 is a graph showing the discharge of the electricity storage device (sample L) obtained in Example 12.

Fig. 15 is a graph showing the discharge of a power storage device (sample N) obtained in Example 14.

Fig. 16 is a graph showing the discharge of the electricity storage device (sample R) obtained in Example 18.

Fig. 17 is a graph showing the discharge of the electricity storage device (sample U) obtained in Comparative Example 1.

18 is a discharge graph of the electricity storage device (sample V) obtained in Comparative Example 2.

Fig. 19 is a graph showing the cycle characteristics of the electricity storage device (Sample A) obtained in Example 1.

Claims (10)

An electric storage device comprising: a positive electrode material containing graphite as a main component; a negative electrode material containing a metal oxide containing at least titanium as a metal element; and an electrolytic solution. The power storage device of claim 1, wherein the metal oxide is titanium oxide. The power storage device of claim 2, wherein the titanium oxide has a crystalline form of anatase and/or rutile. The power storage device of claim 2, wherein the titanium oxide is a layered titanium oxide compound heated. The power storage device of claim 2, wherein the titanium oxide is a secondary particle formed by a primary particle assembly. The power storage device of claim 2, wherein the specific surface area of the titanium oxide is in the range of 0.1 to 500 m ² /g. The power storage device of claim 2, wherein the particle shape of the titanium oxide is flake. The power storage device of claim 1, wherein the metal oxide is a composite oxide of titanium and an alkali metal or alkaline earth metal element. The power storage device of claim 1, wherein the specific surface area of the graphite is in the range of 0.5 to 300 m ² /g. An electric storage device according to claim 1, wherein an electrolyte containing a nonaqueous solvent and a lithium salt is used.